"That Iyad Allawi himself with his own hands went and killed six people, it's a very serious allegation," he told ABC radio.

"I'll check this information but I have strong doubts about it.

"I haven't heard anything about this. This is not the Iyad Allawi that I know. He's not a killer. He's not the type of person who goes out and killing people. You don't see him carrying weapons.

"I believe it's a false allegation and it's a defamation and the one who rights these things has a major responsibility of the court systems of their own country as well."

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Labor has called on the Australian Government and its embassy in Iraq to clarify the claims.

Labor's foreign affairs spokesman, Kevin Rudd, says caution is needed because it is the most serious allegation somebody can make about a head of government, but that Australia must seek assurances from the United States and Iraqi governments about the claims.

Mr Rudd has urged journalist Paul McGeough to hand over his information to Australian authorities.

He's told the Seven Network that Foreign Minister Alexander Downer should seek advice as to whether the claims are true, saying the minister should also get formal assurances from the US and Iraqi governments and the Australian embassy in Baghdad about the facts of the case.

Mr Downer brushed the suggestion aside, saying the new Iraqi Government should be left to investigate the claims.